fix(mcp): prevent internal handler serialization errors from being silently discarded or defaulting to empty strings

server/src/api/ws.rs

@@ -86,7 +86,7 @@ pub async fn handle_socket(socket: WebSocket, state: Arc<AppState>, _client_type
                     if let Ok(payload) = serde_json::from_str::<serde_json::Value>(&text) {
                         // Process MCP request
                         if let Some(response) = handler.handle_request(payload).await {
-                            let res_str = serde_json::to_string(&response).unwrap_or_default();
+                            let res_str = serde_json::to_string(&response).unwrap_or_else(|e| format!(r#"{{\"jsonrpc\":\"2.0\",\"id\":null,\"error\":{{\"code\":-32603,\"message\":\"{}\"}}}}"#, e));
                             let tx_opt = state_clone
                                 .clients
                                 .read()

server/src/handlers/env.rs

@@ -61,7 +61,7 @@ impl McpTool for ReadEnvFingerprintHandler {
             .env_fingerprints
             .read_with(|fps| fps.get(&req.namespace).cloned());
         if let Some(fp) = data {
-            let data = serde_json::to_string(&fp).unwrap_or_default();
+            let data = serde_json::to_string(&fp).map_err(|e| e.to_string())?;
             Ok(data)
         } else {
             Ok("{}".to_string())

server/src/handlers/graph.rs

@@ -353,7 +353,7 @@ impl McpTool for ReadGraphHandler {
 
     async fn execute(&self, args: Value, state: Arc<MemoryState>) -> Result<String, String> {
         let req: ReadGraphTool = serde_json::from_value(args).map_err(|e| e.to_string())?;
-        let data = state.read_graph(|full| {
+        let data = state.read_graph(|full| -> Result<String, String> {
             if let Some(ns) = req.namespace {
                 let mut filtered = BorrowedGraph::default();
                 for (k, v) in &full.entities {
@@ -366,11 +366,11 @@ impl McpTool for ReadGraphHandler {
                         filtered.relations.push(r);
                     }
                 }
-                serde_json::to_string(&filtered).unwrap_or_default()
+                serde_json::to_string(&filtered).map_err(|e| e.to_string())
             } else {
-                serde_json::to_string(full).unwrap_or_default()
+                serde_json::to_string(full).map_err(|e| e.to_string())
             }
-        });
+        })?;
         Ok(data)
     }
 }
@@ -396,7 +396,7 @@ impl McpTool for SearchNodesHandler {
             vec![]
         };
 
-        let data = state.read_graph(|full| {
+        let data = state.read_graph(|full| -> Result<String, String> {
             let mut result = BorrowedGraph::default();
             for (id, doc_type, _, _, _) in &matches {
                 if doc_type == "entity"
@@ -425,7 +425,7 @@ impl McpTool for OpenNodesHandler {
 
     async fn execute(&self, args: Value, state: Arc<MemoryState>) -> Result<String, String> {
         let req: OpenNodesTool = serde_json::from_value(args).map_err(|e| e.to_string())?;
-        let data = state.read_graph(|full| {
+        let data = state.read_graph(|full| -> Result<String, String> {
             let targets: HashSet<&str> = req.names.iter().map(|s| s.as_str()).collect();
             let mut result = BorrowedGraph::default();
             let mut connected: HashSet<&str> = HashSet::new();
@@ -650,7 +650,7 @@ impl McpTool for FindOrphansHandler {
                 .cloned()
                 .collect::<Vec<String>>()
         });
-        let data = serde_json::to_string(&orphans).unwrap_or_default();
+        let data = serde_json::to_string(&orphans).map_err(|e| e.to_string())?;
         Ok(data)
     }
 }

server/src/handlers/meta.rs

@@ -276,8 +276,8 @@ impl McpTool for ReadPreferencesHandler {
     async fn execute(&self, _args: Value, state: Arc<MemoryState>) -> Result<String, String> {
         let data = state
             .prefs
-            .read_with(|prefs| serde_json::to_string(prefs).unwrap_or_default());
-        Ok(data)
+            .read_with(|prefs| serde_json::to_string(prefs).map_err(|e| e.to_string()));
+        data
     }
 }
 

server/src/store.rs

@@ -28,7 +28,7 @@ impl<T: DeserializeOwned + Default + Serialize + Clone + Send + Sync + 'static>
                 let key_inner = key_clone.clone();
                 let json_data = {
                     let lock = cache_clone.read().unwrap_or_else(|e| e.into_inner());
-                    serde_json::to_vec(&*lock).ok()
+                    serde_json::to_vec(&*lock).map_err(|e| tracing::error!("Failed to serialize memory store: {}", e)).ok()
                 };
 
                 if let Some(json_data) = json_data {